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Abstract:

A system of gravel modules to be used atop a room or other enclosure in
which there is a threat of explosion. Each module has a rigid metal box
frame, which contains a two layers of gravel. The lower gravel layer is
screen gravel, and a layer of graded gravel is above the screen gravel.
The box frame has a lower and an upper criss-cross pattern of bridge
cable. A stack of wire mesh and other supporting material is laid over
the lower bridge cable to support the screen gravel, and more wire mesh
is laid over the screen gravel to support the graded gravel. The depths
and grades of gravel are selected according to the type potential
explosion, in terms of explosive fragment sizes and the nature of any
expanding gases.

Claims:

1. A ceiling system for a room in which there is an explosion threat, and
for containing fragments and for diffusing gases resulting from an
explosion, the room having a ceiling support grid, comprising: A tiled
arrangement of gravel modules supported by the ceiling support grid;
Wherein each gravel module comprises a box frame, containing at least a
bottom layer of screen gravel and a top layer of graded gravel; a criss
cross pattern of bridge cable across the bottom of the box frame; a
screen gravel support stack above the first criss-cross pattern of bridge
cable, for supporting the screen gravel, the screen gravel support stack
having a first set of layers of wire mesh, and at least one layer of
closed material; a graded gravel support stack above the screen gravel,
for supporting the graded gravel, and having a second set of layers of
wire mesh; a third stack of wire mesh above the graded gravel; and a
second criss-cross pattern of bridge cable above the third set of layers
of wire mesh and across the top of the box frame.

2. The system of claim 1, wherein the box frame is made from steel
I-beams.

3. The system of claim 1, wherein the screen gravel has a particle size
range of 3/8 inch to 2 inches.

4. The system of claim 1, wherein the graded gravel has a particle size
range of 1 mm to 2 inches.

5. The system of claim 1, wherein the first set of wire mesh layers is
made from welded wire fabric.

6. The system of claim 1, wherein the box frame has a rectangular length
and width.

7. The system of claim 1, wherein the screen gravel layer and the graded
gravel layer are approximately equal in depth.

8. The system of claim 1, wherein the screen gravel support stack further
has at least one layer of wire cloth between the wire mesh and the closed
material.

9. A method of containing fragments and diffusing gases resulting from an
explosion in an enclosed area, comprising: placing a tiled arrangement of
gravel modules over the enclosed area; Wherein each gravel module
comprises a box frame, containing at least a bottom layer of screen
gravel and a top layer of graded gravel; a criss cross pattern of bridge
cable across the bottom of the box frame; a screen gravel support stack
above the first criss-cross pattern of bridge cable, for supporting the
screen gravel, the screen gravel support stack having a first set of
layers of wire mesh, and at least one layer of closed material; a graded
gravel support stack above the screen gravel, for supporting the graded
gravel, and having a second set of layers of wire mesh; a third stack of
wire mesh above the graded gravel; and a second criss-cross pattern of
bridge cable above the third set of layers of wire mesh and across the
top of the box frame.

10. The method of claim 9, wherein the box frame is made from steel
I-beams.

11. The method of claim 9, wherein the screen gravel has a particle size
range of 3/8 inch to 2 inches.

12. The method of claim 9, wherein the graded gravel has a particle size
range of 1 mm to 2 inches.

13. The method of claim 9, wherein the first set of wire mesh layers is
made from welded wire fabric.

14. The method of claim 9, wherein the box frame has a rectangular length
and width.

15. The method of claim 9, further comprising the step of attaching the
edge modules to the enclosure with shock absorbing attachment means.

Description:

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to ballistic containment systems, and more
particularly to architectural structures used to construct rooms in which
explosions are likely to occur.

BACKGROUND OF THE INVENTION

[0002] To avoid disaster, it is sometimes appropriate to provide a
containment system for potential explosions, detonations, or other
energetic events. The explosion may eject large and small objects and
particles (referred to herein collectively as "fragments"), as well as
expanding gases. The containment system should contain the exploding
fragments and should allow the expanding gases to diffuse into the
atmosphere.

[0003] More specifically, an energetic event, such as an explosion, can
expel a wide range of fragments at a wide range of speeds. Relatively
massive fragments, as large as 4.5 kg, can be expelled at speeds below 90
m/s. Lower mass fragments, less than 0.5 kg, can be expelled at speeds of
900 m/s.

[0004] One approach to containing explosions is the use of a "gravel
gertie", such as developed by the Sandia Corporation in the 1950's to
contain nuclear explosions. A gravel gertie is a dome-shaped gravel cover
over an underground room used to assemble nuclear weapons. The gravel
gertie is supported by steel cables strung from concrete walls
surrounding the room. Layers of steel wire mesh are used to contain the
gravel. If an accidental explosion in the room were to occur, the gravel
roof would lift then fall back, filtering the nuclear material from
escaping gasses and preventing them from entering the atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] A more complete understanding of the present embodiments and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings, in which
like reference numbers indicate like features, and wherein:

[0006] FIG. 1 illustrates a single module of the containment system,

[0007] FIG. 2 illustrates a number of modules arranged in a tiled pattern
to form a ceiling over a room in which there is a danger of explosions.

[0008] FIG. 3 is a cross sectional view of the module of FIG. 1.

[0009] FIG. 4 is a more detailed view of a portion of the cross-section of
FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

[0010] As indicated in the Background, gravel domes have been used as an
architectural part of a ballistics containment building. The domes are
designed into the building's structure, and conventionally the dome of
gravel is piled on top of an underground room. The dome of gravel is
designed to heave in the event of an energetic event, and to contain
low-mass high-velocity fragments. Generally, massive relatively
low-velocity fragments have not been a specific design criteria in the
traditional gravel dome designs.

[0011] The invention described herein is directed to a containment system
for a wide range of fragment sizes and velocities that may result from an
explosion. The system is modular, so that containment rooms may be easily
constructed and scaled to a size appropriate for the particular explosion
threat. The modular design permits modules to be easily replaced.

[0012] FIG. 1 illustrates a single module 10 of the containment system. As
explained below, each module 10 consists of a strong box frame 11, filled
with graded and screened gravel sandwiched between layers of bridge
strand and wire mesh. The gravel and the supporting strand and mesh are
engineered to address specified threats (i.e. gas pressures, velocities,
and masses).

[0013] As further explained below in connection with FIG. 2, a typical
application of module 10 is to arrange a number of modules 10 in a tiled
construction that serves as a roof and ceiling for a room in which there
is danger of explosion. One example of such an application is a room that
houses an industrial compressor such as those used in the oil and gas
industry. Another example is a room in which weaponry is assembled or
tested. For these applications, and others, a typical size of module 10
is 10×10 feet (a square rectangle in width and length) with a depth
of 3-4 feet.

[0014] The outer box frame 11 is made from beams of rigid metal, or of
some other material of comparable strength. An example of a suitable
material for the frame 11 is steel I-beams. An I-beam has a strong
central core capped with flanges on either side, and various lengths and
ratings of beams are available. Steel is a typical material used to make
I-beams, because it can withstand heavy loads, but other materials are
sometimes used. Composite I-beams are also available.

[0015] Frame 11 may be made from materials other than I-beams. Regardless
of the material used, frame 11 must support its own weight plus the loads
of a small to nominal containment event without deforming or failing. If
the containment loads are high, then the frame 11 may deform, in which
case module 10 may be replaced. In general, frame 11 should be designed
to meet the scope of the threat in terms of size, strength, and weight.

[0016] FIG. 2 illustrates a ballistic containment room (or other enclosed
area) 20, having a ceiling 21 comprising a tiled arrangement of modules
10. The modules 10 are supported by a structural "ceiling support grid"
(not shown) across the top of the room 20, sufficiently strong to support
the modules. The modules 10 need not be attached to each other or to
their supporting grid, but may be laid atop the grid.

[0017] Alternatively, modules 10 may be bolted to the building, or a shock
absorbing attachment means may be used between the edge modules and the
rest of the building. Examples of simple shock absorbing attachment means
are rubber or elastic isolators. More complex means may be used, such as
tuned spring isolation systems or hammer shock pads. A module may be
sandwiched between pads or isolators, one above and one below. If the
module is impacted, an upper isolator absorbs energy and when the load is
released, the lower isolator absorbs energy and holds the load.

[0018] The modules 10 need not be square in geometry, and may be any shape
suitable for tiling as shown in FIG. 2. Alternative geometries could be
rectangular, hexagonal, or cylindrical.

[0019] Modules 10 are designed to work in the vertical direction. It is
possible to have them at a small angle without a design modification, but
for use at large angles or vertically they would need to be redesigned
with cubical cells which would contain the gravel.

[0020] Modules 10 operate by physically accepting the impact of a threat
and dissipating the energy. Referring again to FIG. 1, various layers of
cable and mesh are illustrated, which absorb explosive energy and contain
the gravel. The explosive energy is transferred to the gravel, the bridge
strand or cable, the module box, and eventually to the building
structure. The building designers and engineers simply need to know the
location of the attachment points and the maximum loads vertically upward
and downward.

[0021] FIGS. 3 and 4 illustrate the layers of cable and mesh for the
example of FIG. 1, as well as the layers of gravel. There are two primary
threats common to most energetic containment events: 1) gas pressure, and
2) ejected fragments. These threats are addressed by each module 10 in
several ways: 1) Bridge cables (top and bottom), 2) screened gravel, 3)
graded gravel, and 4) the frame.

[0022] The lower cables 13 are arranged in a criss-cross pattern and have
two functions. One is to carry the load of the gravel. The second is to
accept the impact loads of a large fragment (i.e. any object too large to
pass between cables). The upper cables 14 carry the load of the gravel
during an energetic event due to fragment impact and gas diffusion
through the gravel. A typical material used for cables 13 and 14 is
bridge strand.

[0023] Module 10 has two layers of gravel, each contained by wire mesh.
The bottom layer of gravel 31 is screened gravel. The top layer of gravel
32 is graded gravel. In the example of this description, the gravel
layers are approximately equal in depth, but their relative depths may
vary. A typical range of sizes (diameter) for the screened gravel is from
3/8 inch to 2 inches. A typical range of sizes (diameter) for the graded
gravel is 1 mm to 2 inches.

[0024] In an explosion, the force due to gas diffusion is primarily upward
and is negligible horizontally because on average the horizontal forces
will cancel each other leaving a pressure differential in the vertical
direction (up) only. The screened gravel layer 31 is engineered to
contain smaller fragments while allowing gasses to diffuse through the
module 10. The depth of the screened gravel layer 31 is dependent on the
threat. The graded gravel layer 32 is designed to contain larger
fragments and provide weight to the module while further allowing gasses
to diffuse through the module into the atmosphere above. Again the depth
of the graded gravel layer 32 is dependent on the nature of the threat.

[0025] To contain and support the screen gravel, module has a "screen
gravel support stack" of various layers. First, a first set of wire mesh
layers 33 is laid over the lower cables 13. In the example of FIGS. 3 and
4, this first set of wire mesh layers 33 has four layers of wire mesh.
Each wire mesh layer has 2×2 openings, and is made from welded wire
fabric (wwf). Welded wire fabric is fabricated from a series of wires
arranged at right angles to each other and welded at all intersections. A
suitable welded wired fabric is made from W1.4 mesh where the "W" number
indicates the size of the cross-sectional area of the wire in hundredths
of an inch.

[0027] The screen gravel layer 31 is placed on top of the felt layer 35.
The depth of layer 31 may very depending on the potential threat, its
force, and size of exploding fragments.

[0028] Above the screen gravel layer 31 is a second set of wire mesh
layers 36 of welded wire fabric. In the example of FIGS. 3 and 4, there
are two layers of wire mesh, made from the same material as stack 33. The
graded gravel layer 32 is placed above, and is supported by wire mesh
layers 36.

[0029] To further contain the graded gravel, a third set of wire mesh
layers 37 is placed above the graded gravel. As stated above, a
criss-cross pattern of cables 14 (the upper cables) lies across the top
of the box frame, over the wire mesh layers 37.

[0030] In sum, the gravel modules 10 address three threat categories:
massive low velocity fragments, low mass high velocity fragments, and gas
overpressure. Massive low velocity fragments are contained directly by
the steel box frame, cables, and mass of the structure. Low mass high
velocity fragments are contained by specified layers of both graded and
screened gravel. Finally, overpressure due to the rapid expansion of
gases is alleviated by diffusion due to the porosity of the gravel
layers. The gravel will begin to heave and the load is taken by the upper
wire mesh layers and bridge strand. Additionally, shockwaves are also
diffused by the gravel layers.